The present invention relates to a phase difference detection device and method for use in position detection and a position detection system which are applicable to detection of both rotational positions and linear positions, such as a rotational position detector like a resolver or synchro, or a linear position detector based on a similar position detecting principle. More particularly, the present invention relates to a technique to detect an absolute position on the basis of an electric phase difference.
Among various induction-type rotational position detectors, one which produces two-phase (sine phase and cosine phase) outputs in response to a single-phase exciting input is commonly known as a “resolver”, and others which produce a three-phase (phases shifted 120° in relation to one another) outputs in response to a single-phase exciting input is known as a “synchro”. The oldest-fashioned resolvers have double-pole (sine pole and cosine pole) secondary windings provided on the stator in such a manner to cross each other at a mechanical angle of 90°, with a primary winding provided on the rotor (the relationship between the primary and secondary windings may be reversed depending on a desired application). However, the resolvers of this type are disadvantageous in that they require brushes for electric contact with the primary winding on the rotor. Brushless resolvers eliminating the need for such brushes are also known, where a rotary transformer is provided on the rotor in place of the brushes.
R/D converters have long been known as a detection system which obtains position detection data in digital form by use of a resolver which produces a two-phase (sine phase and cosine phase) outputs in response to a single-phase exciting input.
U.S. Pat. No. 3,648,042 discloses a technique which provides a rotation angle detection signal of a resolver as an analog voltage signal. Further, U.S. Pat. No. 4,011,440 discloses a technique which generates, on the basis of an output signal from a resolver, a cyclic square-wave signal having a pulse width corresponding to a detected angle and provides an angular rate on the basis of differences between pulse widths in individual cycles.
Another detection system is also known, where the resolver exciting method is modified to produce a single-phase output in response to two-phase exciting inputs so that an output signal containing an electric phase difference angle corresponding to rotational angle θ is obtained to thereby derive digital data indicative of a detected angle θ. Specific examples of the above-mentioned phase difference detection system are disclosed in U.S. Pat. Nos. 4,754,220, 4,297,698, etc.
As known in the art, windings of a sensor such as the resolver tend to undesirably change in impedance under the influence of ambient temperature change, and thus electric phase of A.C. signals induced in a secondary winding subtly fluctuates in response to the temperature change. Additionally, the electric phase of the induced A.C. signals received by a detection circuit varies under the influence of various factors other than a position-to-be-detected, such as ununiform wiring lengths between the windings of the sensor and the detection circuit and delays in various circuit operations. If the phase variation based on the various factors, other than the position-to-be-detected, such as the temperature change is expressed by “±d” for convenience of description, in the former-type detection system, i.e., the R/D converter, the variation amount “±d” is in effect cancelled out and hence has no effect at all on the detecting accuracy. Therefore, it can be seen that the detection system like the R/D converter is a high-accuracy system insusceptible to adverse influence of the ambient temperature change. However, because this detection system is based on a so-called “successive incrementing method” where, as noted earlier, a reset trigger signal is periodically applied to a sequential phase generation circuit at optional timing to reset a phase angle φ to “0” so as to initiate incrementing of the angle φ, and the incrementing of the phase angle φ is stopped upon arrival at “0” of the output of a subtracter to thereby obtain digital data indicative of a detected angle θ, it has to wait for a period from the time when the reset trigger is given to the time when the phase angle φ coincides with the detected angle θ and hence presents poor response characteristics.
On the other hand, in the latter-type detection system, the phase variation amount “±d” based on the non-positional factors (other than the position-to-be-detected) such as temperature change presents a very significant problem that the variation “±d” directly appears as a detection error.
The scheme of generating phase detection data in digital representation permits a high-accuracy detection, but is disadvantageous in that it would require an increased number of detection-signal transmitting lines if the digital detection data are transmitted directly in a parallel fashion.